As analysis techniques have advanced in recent years, techniques are being developed in which microparticles such as biological microparticles (including cells and microorganisms), microbeads, and/or the like, are transported through a flow channel, the microparticles are individually measured in a transport step, and the microparticles that have been measured are analyzed and/or separated/collected. As one representative example of such a technique of analyzing or separating/collecting microparticles using a flow channel, an analysis technique called flow cytometry is being rapidly improved in technology.
Flow cytometry is an analysis technique that analyzes and separates/collects microparticles by introducing analyte microparticles into a fluid in a linear arrangement, irradiating the microparticles with laser light or the like, and thus detecting fluorescence and/or scattered light emitted from each of the microparticles. A process of flow cytometry can be broadly grouped into: (1) water flow part, (2) optical part, (3) electrical/analytical part, and (4) separation/collection part described above.
(1) Water Flow Part
In the water flow part, analyte microparticles are arranged in a linear arrangement in a flow cell (flow channel). More specifically, a sheath flow is introduced into the flow cell at a constant flow velocity, in which condition a sample flow containing the microparticles is gently introduced into a center portion of the flow cell. In this situation, the flows do not mix with each other due to the principle of laminar flow, and thus a flow arranged in layers (laminar flow) is formed. The inflows of the sheath flow and of the sample flow are then adjusted on the basis of the sizes etc. of the analyte microparticles to transport each of the microparticles therethrough in a linear arrangement.
(2) Optical Part
In the optical part, analyte microparticles are irradiated with light, such as laser, and fluorescence and/or scattered light emitted from the microparticles is detected. In the water flow part (1) mentioned above, the microparticles are transported through a laser irradiation portion while each being arranged in a linear arrangement, and each time one microparticle passes therethrough, fluorescence and/or scattered light emitted from that microparticle is detected using an optical detector on a per-parameter basis to analyze characteristics of the individual microparticles.
(3) Electrical/Analytical Part
In the electrical/analytical part, optical information detected in the optical part is converted into an electrical signal (voltage pulse). The electrical signal generated by conversion is digitized by analog-to-digital conversion, and a histogram is computed from the resulting data for analysis, using an analyzing computer and software.
(4) Separation/Collection Part
In the separation/collection part, the microparticles that have undergone measurement are separated and collected. One representative method of separation/collection is a method including positively or negatively charging the microparticles that have undergone measurement, interposing the flow cell between two deflection plates having a potential difference therebetween, and allowing the electrically charged microparticles to be attracted toward one of the deflection plates depending on the electric charge thereof, thereby to perform separation/collection.
A technology for analyzing and separating/collecting microparticles in a flow channel, such as flow cytometry, is widely used in various fields, such as medical, drug discovery, clinical examination, food, agricultural, engineering, forensic medicine, criminal identification fields. Particularly in the medical field, such a technology plays an important role in pathology, tumor immunology, transplantation medicine, genetics, regenerative medicine, chemotherapy, and the like.
Thus, a technology for analyzing and separating/collecting microparticles in a flow channel is needed in a very wide range of fields. Technologies in relation to the processes (1) to (4) described above are also being developed. For example, as a technology in relation to the (1) water flow part described above, Patent Document 1 discloses a technology for controlling a flow velocity of a sheath fluid by providing a pressure sensor in a flow channel of the sheath fluid, and by changing a value of the pressure exerted on the sheath fluid on the basis of the water pressure sensed by the pressure sensor.